Light transmitting modules with optical power monitoring

ABSTRACT

An optical module, such as a package for a vertical cavity surface emitting laser diode (VCSEL) or other light emitting device, includes monitoring of the emitted optical power by tapping the transmitted beam. The module includes a substrate, which carries the light emitting device and an optical monitor. In addition, the module includes a transparent plate with at least two reflective regions that together redirect part of the light from the light emitting device to the optical monitor.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a divisional of U.S. Ser. No. 10/777,583, filed Feb.12, 2004

BACKGROUND

This disclosure relates to light transmitting modules with optical powermonitoring.

In housings for light emitting devices, it sometimes is desirable to beable to monitor the emitted optical power. For certain devices, it isalso desirable or necessary to draw the monitored power directly fromthe transmitted optical beam.

Several techniques have been suggested to realize housings for lightsources with power monitoring obtained directly from the transmittedbeam. However, sometimes it is difficult to achieve a design that doesnot overly restrict the possible positions of the radiation sensitivecomponent relative to the light emitter and that can compensate fordivergence angle changes. It also would be desirable to achieve asimple, inexpensive design to monitor the emitted optical power in a waythat allows standard components to be used as monitoring receivers.

SUMMARY

The present invention relates to an optical module, such as a packagefor a vertical cavity surface emitting laser diode (VCSEL) or otherlight emitting device, that includes monitoring of the emitted opticalpower by tapping the light from the light emitting device.

The module may include a substrate that carries the light emittingdevice and an optical monitor. In addition, the module includes atransparent plate with at least two reflective regions that togetherredirect part of the light from the light emitting device to the opticalmonitor.

In one implementation, an optical module includes a substrate thatcarries a light emitting device and an optical monitor. The moduleincludes a plate that is positioned in a path of light emitted by thelight emitting device and that is transparent to light emitted by thelight emitting device. Thus, light emitted by the light emitting devicemay be transmitted entirely the plate. The plate includes reflectiveregions, a first one of which is located to reflect some of the lightemitted by the light emitting device and a second one of which islocated to receive light reflected by the first reflective region and todirect the received light to the optical monitor.

In various implementations, one or more of the following features may bepresent. For example, the first and second reflective regions may belocated on the same side of the plate and may be located, for example,on a side of the plate that is further from the light emitting deviceand the optical monitor. The first and second reflective regions maycomprise grooves in a surface of the plate. The reflective regions mayinclude angled facets that provide total internal reflection of lightimpinging on the facets. The first reflective region preferably isoffset from an optical axis of the light emitting device. The plate alsomay include a focusing lens to focus light from the light emittingdevice that is transmitted through the plate. The focusing lens may belocated on a same side of the plate as the first and second reflectiveregions.

The light emitting device and optical monitor may be mounted on thesubstrate or integrated into the substrate. The substrate may include acavity within which the light emitting device and optical monitor areenclosed. In some implementations, the plate may be positioned over thecavity and may be sealed hermetically to the substrate. The substratealso may include hermetic, electrical feed throughs to the lightemitting device and optical monitor.

According to another aspect, an optical assembly includes an opticalmodule comprising a housing in which a light emitting device and anoptical monitor are mounted. The assembly also includes amulti-functional piece having a cavity to receive the optical module, afirst reflective surface to reflect light from the light emitting devicein a direction substantially perpendicular to a direction of lightemitted by the light emitting device, and a second reflective surface toreflect some of the light from the first reflective surface to theoptical monitor.

The light emitting device and the optical monitor may be hermeticallysealed in the optical module. In some implementations, themulti-functional piece may include a receptacle for an optical fiberferrule. A fiber may be positioned in the receptacle to receive at leastsome of the light reflected by the first reflective surface and notsubsequently reflected by the second reflective surface. The secondreflective surface may be positioned to reflect light from the firstreflective surface in a direction substantially perpendicular to adirection of light reflected by the first reflective surface.

Methods for monitoring light from a solid state device also aredescribed.

Advantages that may be obtained in some implementations include thefollowing. For example, additional parts may not be required to obtainthe power monitoring because the reflectors can be integrated intocomponents that already are required (e.g., lens plates or sealinglids). Processing of the reflectors may be simplified because onlysurface structuring on a single surface is required for manyimplementations, and the deposition of additional reflective materialscan be avoided in some cases.

The optical modules and assemblies described here can help improveachieving monitored power with low aberration of the transmitted beamand can help compensate for divergence angle fluctuations. Furthermore,the modules may provide greater flexibility in the placement of themonitoring receiver with a small distance between the reflector plateand the light emitter.

Other features and advantages will be readily apparent from thefollowing detailed description, the accompanying drawings and theclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a housing for a light emitting device and an opticalpower monitor according to one implementation of the invention.

FIG. 2 illustrates an example of a sealing plate with reflectivesurfaces for the housing of FIG. 1.

FIG. 3 illustrates optical paths for the monitored light in the housingof FIG. 1.

FIG. 4 illustrates a sub-mount for a light emitting device, an opticalmonitor and other components.

FIG. 5 illustrates an assembly according to another implementation ofthe invention with reflective surfaces integrated into a lens plate atopa sealed hermetic housing.

FIG. 6 illustrates an example of a lens plate for the assembly of FIG.5.

FIG. 7 illustrates an implementation of a non-hermetic housing accordingto the invention.

FIGS. 8 and 9 illustrate front and back views, respectively, of thenon-hermetic sub-mount.

FIGS. 10 and 11 illustrate an implementation which allows the light tobe transmitted horizontally out of the package.

DETAILED DESCRIPTION

As shown in FIG. 1, a light transmitting module includes a housing for alight emitting device, such as a vertical cavity surface emitting laserdiode (VCSEL) 2. Other semiconductor or solid state light emittingdevices may be used as well. The housing includes a substrate 11, which,in the illustrated implementation, serves as a sub-mount for the lightemitting device 2, and an optical monitor 1 with a radiation sensitivearea. In other implementations, the light emitting device and monitormay be integrated directly into the substrate. The optical monitor maybe integrated, for example, into the same substrate that carries thelight emitting device.

In FIG. 1, the housing also includes a sealing plate 4 that istransparent to light emitted by the light emitting device 2 and thatincludes at least two reflective regions that together redirect some ofthe transmitted light back onto the optical monitor 1. As shown in FIG.1, the plate 4 includes reflective surfaces 5, 6 and 8. In theillustrated implementation (see FIGS. 1 and 2), the reflective regionsare formed by facets or grooves 20, 21 provided in the same surface ofthe plate 4, which may be hermetically sealed to the substrate 11.

In the implementation of FIG. 1, instead of directly redirecting thereflected light onto the monitoring receiver 1, the first reflectivesurface 5 directs the light in an approximately perpendicular directionto the original beam. Therefore the size, position and shape of thefirst reflective surface may be chosen to optimize the monitored powerand to minimize the dependence of the monitored power on divergenceangle fluctuations of the emitted beam. The second reflective surface 6directs the radiation from the first reflective surface 5 back towardthe sub-mount and to the monitoring receiver 1. The reflective surface 6may be shaped to provide some focusing capability.

With reference to FIG. 1, some of the light rays emitted from the source2 propagate close to the optical axis 37, travel substantially straightthrough the transparent plate 4 and exit the plate at the straight outersurface 8, preferably with low reflection losses. The outer surface 8 ofthe plate 4, which may be made, for example, of silicon or glass, mayinclude an anti-reflection coating to help reduce such losses.

The distance between the first reflective surface 5 and the optical axis37 is indicated by arrows 17, and the size of the reflective region isindicated by arrows 18. As illustrated by FIG. 3, some light rays thatare offset from the optical axis 37 strike the reflective surface 5 andare internally reflected. The reflected rays subsequently strike thesecond reflective surface 6, in some cases after being reflected fromthe outer surface 8 of the plate 4 as a result of the shallow incidentangle. The second reflective surface 6 directs at least some of thelight rays 7 toward the monitoring detector 1. A reflector designcapable of compensating for divergence angle changes can be realized byproperly choosing the size 18 and position 17 of the reflective surface5. The position of the second reflective surface 6 (indicated by thearrows 16) can be chosen for optimum coupling to the receiver device 1on the substrate 11. Although the implementation of FIGS. 1-3 shows thegrooves 20, 21 for the reflective surfaces 5, 6 in the exterior surfaceof the plate 4, in other implementations the reflective surfaces fordirecting light back to the monitor 1 may be provided at an innersurface of the plate (i.e., the surface closer to the device 2 and themonitor 1).

The substrate 11 may include, for example, double-layer silicon on aninsulator. A wet etching technique may be used to form a groove or othercavity 19 in which the light emitting device 2 and optical monitor 1 areto be mounted. Wet etching also may be used to provide hermetic,electrical feed throughs 12. Slanted sidewalls are preferred to allowfor the use of lithography. If different materials, such as glass orceramic, are used for the substrate 11, then other techniques may beemployed to form the groove and feed throughs. Metal subsequently may bedeposited to seal the feed throughs 12 hermetically and to formelectrical lines 15 and pads 13. The emitter 2 and the receiver 1 thenare soldered or otherwise bonded to the membrane 35. Optionally,electrical contacts may be provided by bond pads 14 below the device 2and monitor 1. Additional electrical contacts 10 may be formed by bondwires from the devices 1, 2 to the upper edge of the groove 19. Ifsilicon (e.g., a (100) wafer) is used for the sealing plate 4, thereflective surfaces 5, 6 may be formed, for example, by a wet etch ofV-grooves 20 and 21, as shown in FIG. 2. In the case of wet-etchedcrystalline plates, the angle of the reflective surfaces is determinedby the crystal planes.

As shown in FIG. 4, the substrate 11 also may include additionalcavities for other active and passive components, such as a driver chip22 for the laser 2, and inductive coils 24. Those components, as well asothers such as capacitors, can share a common package ground 23. Thecavities on the substrate may be sealed hermetically, individually bysingle lids or together by a large lid. The hermetic seal may beprovided, for example, by using a solder sealing-ring deposited eitheron the lid or the substrate.

A second implementation is illustrated in FIGS. 5 and 6 and includes ahousing for a light emitting device 2 and an optical monitor 1 mountedon a substrate 11. The cavity 19 in which the light emitting device 2and optical monitor 1 are located may be sealed hermetically by a first(sealing) plate 25, which is transparent to light emitted by the device2. A second (reflector) plate 27, which also is transparent to lightemitted by the device 2, includes reflective surfaces 29, 30 and 31 toredirect light emitted from the device 2 back to the monitor 1. Thesecond plate 27 is mounted to the first plate 25. The reflectivesurfaces 29, 30, and 31 function in a manner similar to the surfaces 5,8 and 6 described above in connection with FIG. 1. In particular, somelight rays that are offset from the optical axis of the light emittingdevice 2 strike the first reflective surface 29 and are internallyreflected. The reflected rays subsequently strike the second reflectivesurface 31, in some cases after being reflected from the outer surface30 of the plate 27 as a result of the shallow incident angle. The secondreflective surface 31 directs at least some of the light rays toward themonitoring detector 1.

The second reflective surface 31 may be curved to help focus the lightat the optical monitor 1. Alignment marks 33 (FIG. 6) for fiberreceptacles also may be added to the external reflector plate 27, whichmay be molded, for example, from plastic, glass or othersurface-machined materials. The plate 27 also may include an imaginglens 28 to focus the transmitted radiation.

According to another implementation illustrated in FIGS. 7, 8 and 9, thereflector plate 27 may be mounted on a non-hermetic sub-mount withoutthe addition of a separate sealing plate 25 as used in theimplementation of FIG. 5. The reflector plate 27 in FIG. 7 is similar tothe one described above in connection with FIG. 5, but may includeadditional standoffs 39. If the substrate 11 comprises silicon, thenetching can be performed simultaneously from both sides to create thefront side cavity 19, two back side cavities 32, and through holes 34.Further processing of the sub-mount may be performed as described abovein connection with FIG. 1.

The use of two or more reflective surfaces can allow for a wide range ofmonitored power levels and for compensation of variations in themonitored power resulting from fluctuations in the beam divergenceangle. It also allows for flexibility in placement of the radiationsensitive element 1 relative to the light emitting element 2.

Fabrication of the reflectors can be relatively simple. If the incidentangles of radiation rays on the reflective areas are on the order of 45°or less, it is possible, for many plate materials (e.g., silicon, glass,polymers) to employ total internal reflection for redirecting the light(assuming the beam originates from the medium with the higher refractiveindex). For some implementations, that may eliminate the need to depositreflective materials on the surfaces of the angled facets, although thatstill may be done. The power monitoring techniques may be used in bothsingle-mode and multi-mode applications, with the monitored power drawndirectly from the transmitted optical beam.

Although the plates (i.e., sealing plates and reflector plates) aretransparent to light emitted by the light emitting device 2, the platesneed not be transparent to all wavelengths of light emitted by thedevice. The plates should be transparent at least to the wavelength(s)of interest, in other words, the wavelengths that are to be transmittedthrough the plates to the outside and that are to be monitored by theoptical monitor 1. Of course, in some implementations, the plates may betransparent to all (or substantially all) wavelengths of light emittedby the light emitting device 2.

In certain applications, it may be desirable to redirect and transmitthe light beam in the horizontal direction, rather than vertically outof the package. This can be achieved, for example, by a multi-functionalpart that combines the functionality of a receptacle for a fiberferrule, imaging of the optical beam through one or more lenses,redirection of the light by 90°, and power monitoring. Themulti-functional piece 40 may be made, for example, from molded plastic.Alternatively, the piece 40 may be machined using other materials.

An example of such a multi-functional part 40 is shown in FIGS. 10 and11. The part 40 includes a cavity to receive an optical module thatincludes a hermetically sealed housing in which a light emitting device2 and optical monitor 1 are encapsulated. As in the implementationsdescribed above, the light emitting device and optical monitor may bemounted on a substrate 11 that includes externally accessible electricalcontacts (not shown in FIGS. 10 and 11). The device 2 emits light in thevertical direction. The optical module also includes a cover, such asplate 25, that is transparent to light emitted by the device 2. A lens42 may be provided as part of the optical module to collimate the lightbeam from the device 2.

The multi-functional part 40 includes at least two reflective surfaces44, 46 to redirect some or all of the light from the device 2. Thereflective surfaces may comprise, for example, grooves or facets. Thefirst reflective surface 44 is positioned so as to intercept light fromthe device 2 and to redirect the light at about a 90° angle. The lightreflected by the first surface 44 is partially intercepted andredirected by the second surface 46 toward the optical monitor 1. Someof the light reflected by the first surface 44 travels in the horizontaldirection and may be coupled, for example, to an optical fiber (notshown). In the illustrated implementation, the part 40 also includes areceptacle 50 for a fiber ferrule. A lens surface 52 may be provided tofocus light onto the fiber.

Other implementations are within the scope of the claims.

1. An optical assembly comprising: an optical module comprising ahousing in which a light emitting device and an optical monitor aremounted; a multi-functional piece comprising: a cavity to receive theoptical module; and a first reflective surface to reflect light from thelight emitting device in a direction substantially perpendicular to adirection of light emitted by the light emitting device such that someof the light reflected by the first reflective surface is received by anoptical component with an optical axis aligned substantially along theperpendicular direction; and a second reflective surface to reflect someof the light from the first reflective surface to the optical monitor.2. The optical assembly of claim 1 wherein the multi-functional pieceincludes a receptacle for an optical fiber ferrule to facilitatepositioning of a fiber to receive at least some of the light reflectedby the first reflective surface and not subsequently reflected by thesecond reflective surface.
 3. The optical assembly of claim 1 whereinthe second reflective surface is positioned to reflect light from thefirst reflective surface in a direction substantially perpendicular to adirection of light reflected by the first reflective surface.
 4. Theoptical assembly of claim 3 wherein the light emitting device and theoptical monitor are hermetically sealed in the optical module.
 5. Theoptical assembly of claim 1 wherein the optical component comprises anoptical fiber.
 6. The optical assembly of claim 1 wherein the firstreflective surface comprises a groove or facet.
 7. The optical assemblyof claim 6 wherein the second reflective surface comprises a groove orfacet.
 8. The optical assembly of claim 7 wherein the multi-functionalpiece is composed of plastic.
 9. The optical assembly of claim 1 whereinthe light emitting device is a semiconductor laser diode.